Friction stir welding tool and friction stir welding method for plates with different thicknesses

Abstract

The invention discloses a friction stir welding tool and a friction stir welding method for plates with different thicknesses. The friction stir welding tool comprises a handle portion, the handle portion is connected with a stirring needle through a connecting piece, the stirring needle is composed of a cylindrical section and a hemispherical section, the connecting portion of the cylindrical section and the hemispherical section is in smooth transition, and only the hemispherical section can be inserted into a workpiece in the friction stir welding process. The friction stir welding method for the non-uniform-thickness plates comprises the steps that the friction stir welding tool is controlled to rotate and press downwards, so that the hemispherical section of the stirring needle is inserted into a thin plate and a thick plate by a preset depth, and welding is conducted along a preset path. The non-uniform-thickness plate butt welding device can achieve stable welding of non-uniform-thickness plate butt welding seams, can be suitable for butt welding of plates with various thickness differences, and solves the technical problem that in the existing non-uniform-thickness plate welding process, a downward-concave structure is likely to be formed on the surfaces of the welding seams.

Description

Technical Field

[0001] This invention relates to the field of friction stir welding technology, specifically to a friction stir welding tool and a friction stir welding method for non-uniform thickness plates. Background Technology

[0002] The geometry, size, and characteristics of friction stir welding tools affect the generation of welding heat and material flow, thus influencing the stability and strength of the joint. In traditional friction stir welding, the shoulder is typically designed as a flat surface or a concave / convex shape with a small angle, making it unsuitable for butt welding of plates of unequal thickness. More importantly, the friction between the shoulder and the plate surface generates a large amount of heat, creating a heat-affected zone (HAZ) around the weld area. This zone typically has larger grain sizes and lower hardness, becoming a weak point in the weld joint. Furthermore, to reduce the forging force during the tool's insertion, the stirring pin diameter is usually small, while bearing a large cyclic load, resulting in a higher risk of failure.

[0003] Existing literature CN110814509A discloses a tool and method for bladeless and thinning bladeless friction stir welding. It utilizes a pressure plate to press the workpiece onto a substrate. A mating groove is formed on the pressure plate, and a trapezoidal pressure plate mating body is placed within the groove. The bladeless stirring pin and its mating pressure plate can be designed according to the thickness and shape variations of the workpiece, achieving bladeless and thinning bladeless friction stir welding. However, this method essentially replaces the blade with a mating body, making it more similar to static bladeless friction stir welding. Furthermore, it requires additional design of the pressure plate, mating body, and accompanying welding block, making the clamping process complex. It also faces the risk of plasticizing material clogging the mating groove during welding.

[0004] Another existing patent, CN103071916A, discloses a shoulderless friction stir welding head that can reduce flash. The stirring pin has a spatial curved rotation structure, with its root diameter connected to the front cylinder and an annular protrusion at the edge. The stirring pin has a circular arc-shaped pin tip. The friction stir welding parameters are a welding tilt angle of 2.5° (the welding tool tilts 2.5° towards the weld, i.e., the angle between the welding tool axis and the weld centerline is 87.5°). This solution solves the problems of large thinning on the advancing side and large flash on the retreating side by improving the surface shape and structure of the stirring pin of the shoulderless friction stir welding head, and can be used to weld plates with inconsistent thicknesses. However, its stirring pin surface structure is extremely complex, with poor versatility (only suitable for welding plates with specific thickness differences), and the welding tool experiences great resistance during welding, resulting in poor weld surface quality. Summary of the Invention

[0005] At least in response to the technical problems mentioned in the background art, the present invention aims to provide a friction stir welding tool and a friction stir welding method for non-uniform thickness plates.

[0006] A friction stir welding tool includes a shank, and a stirring pin is connected to the shank via a connector. The stirring pin is composed of a cylindrical section and a hemispherical section. The connection between the cylindrical section and the hemispherical section is a smooth transition, and only the hemispherical section can penetrate into the workpiece during the friction stir welding process.

[0007] Preferably, the connector adopts a cylindrical structure, with the upper half of the cylindrical section extending into the connector and the cylindrical section being fixedly connected to the connector by a set screw.

[0008] Preferably, the diameter of the cylindrical segment is equal to the diameter of the hemispherical segment.

[0009] A method for friction stir welding of non-uniform thickness plates using the aforementioned friction stir welding fixture, comprising the following steps: Step 1: Prepare the thin and thick plates to be welded and pre-treat them; Step 2: Fix the thin and thick plates onto the pad, and fix the pad onto the horizontal worktable; install the friction stir welding tool on the spindle of the friction stir welding machine, and adjust the spindle angle to tilt the axis of the friction stir welding tool. Step 3: Start the friction stir welding machine, set the friction stir welding process parameters, control the rotation and pressing of the friction stir welding tool, so that the hemispherical section of the stirring needle penetrates into the predetermined depth in the thin and thick plates, and welds along the preset path; Step 4: After welding is completed, keep the friction stir welding tool away from the plate, turn off the friction stir welding machine, and place the welded plate in the air to cool to room temperature to obtain the friction stir weld.

[0010] Preferably, the radius of the hemispherical segment is greater than or equal to 2.5 times the thickness of the thin sheet.

[0011] To address the technical challenge of creating a concave structure on the weld surface during welding of non-uniform thickness plates, the axis of the friction stir welding tool is tilted towards the direction of the thicker plate at an angle of 5°, and the axis of the friction stir welding tool is perpendicular to the center line of the weld.

[0012] To further improve the surface quality of the weld, the rotation speed of the friction stir welding tool is 400~600 rpm and the forward speed is 30~70 mm / min during the welding process; when the thin plate is located to the right of the thick plate and the weld direction is front-to-back, the rotation direction of the friction stir welding tool is counterclockwise.

[0013] Preferably, the predetermined depth to which the hemispherical segment is inserted into the thick plate is 1 / 3 of the radius of the hemispherical segment; the height difference between the thin plate and the thick plate is no more than 1 mm.

[0014] In this invention, the surface of the friction stir weld is generally inclined with an arc-shaped convex structure. The low point of the arc-shaped convex structure is flush with the top surface of the thin plate, and the high point of the arc-shaped convex structure is located between the thin plate and the thick plate.

[0015] Beneficial Effects: The solution of this invention not only enables stable welding of butt joints in plates of unequal thickness, but is also applicable to butt joint welding of plates with various thickness differences. In this invention, the hemispherical segment of the stirring pin simultaneously performs the functions of the stirring pin and the shoulder in the traditional friction stir welding fixture structure, reducing the contact area between the welding fixture and the material. This effectively reduces heat generation during the welding process, decreases the range and peak temperature of the heat-affected zone, and also limits the overflow of plasticized materials. The failure risk of the stirring pin in this invention is extremely low, the resistance during the welding process is small, stress concentration during welding is avoided, and the friction stir welding fixture has high load-bearing capacity. The friction stir welding fixture of this invention has a simple structure, good versatility (applicable to butt joint welding of plates with various specific thickness differences), low resistance during welding, and good weld surface quality. More importantly, this invention also solves the technical problem of easily forming concave structures on the weld surface during the welding of plates of unequal thickness. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the friction stir welding process for plates of non-uniform thickness in the embodiment; Figure 2 This is a schematic diagram of the stirring pin of the friction stir welding fixture in the embodiment; Figure 3 A schematic diagram of material flow around the stirring pin during friction stir welding of plates of different thicknesses. Figure 4 This is a partially enlarged view of the friction stir welding process of non-uniform thickness plates in the embodiment; Figure 5 This is a schematic diagram of the weld morphology obtained in Example 1; Figure 6 This is a schematic diagram of the weld morphology obtained in the comparative embodiment; Figure 7 This is a schematic diagram of the weld surface obtained in Example 1; Figure 8 This is a surface view of the weld obtained in the comparative embodiment; Figure 9 This describes the resistance experienced by the friction stir welding tool during the welding process in Example 1. Figure 10 To illustrate the resistance experienced by the friction stir welding tool during the welding process in the comparative examples; Reference numerals: 1—Handle, 2—Connector, 3—Setting screw, 4—Stirring pin, 41—Cylindrical section, 42—Hemispherical section, 43—Milled plane, 5—Clamping plane, 6—Thin plate, 7—Thick plate, 8—Clamping block one, 9—Clamping block two, 10—Backing plate, 11—Arc-shaped convex structure of weld surface, 12—S-shaped curved surface structure of weld surface. Detailed Implementation

[0017] The following detailed description provides further details on specific implementation methods. Example 1

[0018] Combination Figures 1 to 4 As shown, a friction stir welding tool includes a handle 1 with a clamping plane 5. The handle 1 is connected to a stirring pin 4 via a connector 3. The stirring pin 4 is composed of an integrally formed cylindrical section 41 and a hemispherical section 42. The radius of the hemispherical section 42 is 2.5 times the thickness of the thin sheet 6. The diameter of the cylindrical section 41 is equal to the diameter of the hemispherical section 42. The connection between the cylindrical section 41 and the hemispherical section 42 is a smooth transition, and only the hemispherical section 42 can penetrate into the workpiece during friction stir welding. The connector 3 has a cylindrical structure. The cylindrical section 41 has a milled plane 43. The upper half of the cylindrical section 41 extends into the connector 3 and is fixedly connected to the connector 3 by a set screw 3, which abuts against the milled plane 43.

[0019] A method for friction stir welding of non-uniform thickness plates using the friction stir welding fixture in this embodiment includes the following steps: Step 1: Prepare the thin plate 6 and thick plate 7 to be welded and pre-treat them; specifically: the thin plate 6 is a 3mm thick aluminum alloy and the thick plate 7 is a 3.5mm thick aluminum alloy. Use mechanical grinding to clean the oxide film on the surface of the thin plate 6 and thick plate 7, and use organic solvent (anhydrous ethanol or acetone solution) to wipe the surface of the thin plate 6 and thick plate 7 to remove the oil and metal powder adhering to the surface. Step 2, combined Figure 1 As shown, the thin plate 6 and the thick plate 7 are fixed on the pad 10 using clamping block 8 and clamping block 9, and the pad 10 is fixed on the horizontal worktable; the friction stir welding tool is installed on the spindle of the friction stir welding machine (the handle 1 is assembled with the spindle of the friction stir welding machine), and the spindle angle is adjusted to tilt the axis of the friction stir welding tool. Step 3: Start the friction stir welding machine, set the friction stir welding process parameters (the rotation speed of the friction stir welding tool is 500 rpm and the forward speed is 50 mm / min during the welding process), control the rotation of the friction stir welding tool and press it down so that the hemispherical section 42 of the stirring needle 4 penetrates into the thin plate 6 and the thick plate 7 to a predetermined depth and welds along the preset path. In this step, the axis of the friction stir welding tool is tilted towards the direction of the thick plate 7 at an angle of 5°, and the axis of the friction stir welding tool is perpendicular to the center line of the weld; combined with Figure 5 As shown, the predetermined depth to which the hemispherical segment 42 penetrates the thick plate 7 is 1 / 3 of the radius of the hemispherical segment 42 (specifically, the radius of the hemispherical segment 42 is 7.5 mm, and the predetermined depth to which the hemispherical segment 42 penetrates the thin plate is 2.5 mm); the thin plate 6 is located to the right of the thick plate 7, and during welding, the rotation direction of the friction stir welding tool is counterclockwise. Figure 4 The direction indicated by the middle arrow represents the rotation direction of the friction stir welding tool; the welding direction is the same as the rotation direction. Step 4: After welding, keep the friction stir welding tool away from the plate, turn off the friction stir welding machine, and place the welded plate in the air to cool to room temperature. This yields a friction stir weld with an overall inclined arc-shaped convex surface structure 11 (weld cross-section direction). The resulting weld morphology is as follows: Figure 5 and Figure 7 As shown, the resulting weld surface has almost no thinning area (thinning amount less than 0.2 mm).

[0020] In this embodiment, by using a welding tool axis tilted towards the direction of the thick plate 7 and a hemispherical segment 42 tilted at a specific angle and in a specific direction for insertion welding, not only can the plasticized material be fully reflowed and backfilled, forming a friction stir weld with an overall inclined arc-shaped convex surface structure, but it also cleverly solves the technical problem of easily forming a concave structure on the weld surface during the welding process of non-uniform thickness plates.

[0021] Combination Figure 3 As shown, during the welding process, the area where the stirring pin 4 acts can be divided into regions A, B, and C. The rotation axis of the stirring pin 4 is the central axis of its cylindrical section 41. Due to the 5° angle between the axis of the stirring pin 4 and the vertical direction, the flow state of the plasticized material is not horizontal; the direction of the driving force it experiences forms a certain angle with the horizontal plane. In region A, the material on the advancing side flows to the retreating side under the driving action of the stirring pin 4. Theoretically, it would flow to region D during its return flow to the advancing side, i.e., be extruded from the weld. However, in reality, due to the effects of gravity, friction from the surrounding cold metal, and its own viscous resistance, most of the material can be backfilled into the advancing side weld, with only a small amount overflowing as flash. Thinning of the weld on the advancing side is almost nonexistent. In region B, the force and flow of the material are similar to those in region A, but the plasticized material is completely retained in the weld. In region C, since the contact surface between the material and the hemispherical section 42 of the stirring pin is a dome surface, its flow direction can be approximated as horizontal.

[0022] Traditional friction stir welding tools are typically only suitable for butt joints of thin plates of uniform thickness, and each tool is limited to a single plate thickness, exhibiting poor adaptability to variations in plate thickness. The stirring pin of this invention features a hemispherical portion, enabling a smooth transition in butt welds of plates with varying thicknesses, and can be used for welding plates with diverse thicknesses. This invention significantly reduces the contact area between the friction stir welding tool and the workpiece. In traditional friction stir welding, the shoulder generates significant heat through friction with the surface of the metal to be welded, resulting in a heat-affected zone (HAZ) with coarse grains and low hardness around the stirring pin's action area, leading to deterioration of the joint performance. In this invention, the hemispherical tip of the stirring pin simultaneously functions as both the stirring pin and the shoulder in a traditional friction stir welding tool, reducing the contact area between the tool and the material. This effectively reduces the extent and peak temperature of the HAZ. Simultaneously, the spherical surface, while engaging in friction with the workpiece, also helps limit the overflow of plasticizing materials, preventing weld thinning.

[0023] To reduce the upsetting force during the stirring pin insertion process, traditional flat-end stirring pins typically have a small diameter, roughly equal to or slightly larger than the plate thickness. This leads to a higher risk of failure for the stirring pin under significant torque and triaxial forces during welding. In contrast, the hemispherical segment used in this invention reduces resistance during the insertion process. Its radius is more than 2.5 times the plate thickness, preventing stress concentration during welding and resulting in a high load-bearing capacity for the stirring pin.

[0024] The friction stir welding fixture and welding method provided by this invention eliminate the need to grind the welding area of ​​non-uniform thickness plates to the same thickness before welding. It has strong adaptability to plate thickness and can be applied to butt welding of non-uniform thickness plates. At the same time, it can reduce the range of the welding heat-affected zone and lower the welding peak temperature. Moreover, the welding fixture has high load-bearing capacity and low failure risk, further simplifying the friction stir welding process, improving welding efficiency and saving costs, and expanding the breadth and depth of the application of friction stir welding technology.

[0025] Comparative embodiment, referring to embodiment 1, differs from embodiment 1 in that: the axis of the friction stir welding tool is inclined towards the direction of the thin plate 6, and the resulting weld is as follows: Figure 6 and Figure 8 As shown, one side of the weld surface has a significant thinning area, with a thinning amount of 0.7~1mm; the resulting weld has an S-shaped curved surface structure 12 (weld cross-section direction).

[0026] During the friction stir welding tool insertion and welding stages, the friction stir welding tool in Example 1 experiences the following resistance: Figure 9 As shown, the resistance experienced by the friction stir welding tool in the comparative embodiment is as follows: Figure 10 As shown. The results show that the resistance experienced by the friction stir welding tool in Example 1 is significantly lower than that experienced by the friction stir welding tool in the comparative example.

Claims

1. A friction stir welding tool, comprising a shank (1), characterized in that: The handle (1) is connected to a stirring needle (4) via a connector (3). The stirring needle (4) is composed of a cylindrical section (41) and a hemispherical section (42). The connection between the cylindrical section (41) and the hemispherical section (42) is a smooth transition, and only the hemispherical section (42) is used to penetrate into the workpiece during the friction stir welding process.

2. The friction stir welding tool according to claim 1, characterized in that: The connector (3) adopts a cylindrical structure. The upper part of the cylindrical section (41) extends into the connector (3) and is fixedly connected to the connector (3) by the set screw (3).

3. The friction stir welding tool according to claim 1, characterized in that: The diameter of the cylindrical segment (41) is equal to the diameter of the hemispherical segment (42).

4. A method for friction stir welding of non-uniform thickness plates using the friction stir welding fixture according to any one of claims 1-3, characterized in that the steps include... include: Step 1: Prepare the thin plate (6) and thick plate (7) to be welded, and pre-treat them; Step 2: Fix the thin plate (6) and the thick plate (7) on the pad (10), and fix the pad (10) on the horizontal worktable; install the friction stir welding tool on the spindle of the friction stir welding machine, and adjust the spindle angle to tilt the axis of the friction stir welding tool; Step 3: Start the friction stir welding machine, set the friction stir welding process parameters, control the friction stir welding tool to rotate and press down, so that the hemispherical section (42) of the stirring needle (4) penetrates into the thin plate (6) and the thick plate (7) to a predetermined depth, and welds along the preset path; Step 4: After welding is completed, keep the friction stir welding tool away from the plate, turn off the friction stir welding machine, and place the welded plate in the air to cool to room temperature to obtain the friction stir weld.

5. The friction stir welding method for non-uniform thickness plates according to claim 4, characterized in that: The radius of the hemispherical segment (42) is greater than or equal to 2.5 times the thickness of the thin plate (6).

6. The friction stir welding method for non-uniform thickness plates according to claim 4, characterized in that: The axis of the friction stir welding tool is inclined towards the direction of the thick plate (7) at an angle of 5°, and the axis of the friction stir welding tool is perpendicular to the center line of the weld.

7. The friction stir welding method for non-uniform thickness plates according to claim 4, characterized in that: During the welding process, the rotation speed of the friction stir welding tool is 400~600 rpm and the forward speed is 30~70 mm / min; when the thin plate (6) is located to the right of the thick plate (7) and the weld direction is front and back, the rotation direction of the friction stir welding tool is counterclockwise.

8. The friction stir welding method for non-uniform thickness plates according to claim 7, characterized in that: The predetermined depth to which the hemispherical segment (42) is inserted into the thick plate (7) is 1 / 3 of the radius of the hemispherical segment (42); the height difference between the thin plate (6) and the thick plate (7) is no more than 1 mm.

9. The friction stir welding method for non-uniform thickness plates according to any one of claims 5-8, characterized in that: The surface of the friction stir weld has an overall inclined arc-shaped convex structure.

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